1. Field of the Invention
The present invention relates to a two-phase excitation linear motor.
2. Description of the Related Art
A linear motor has a simple structure, comprises a small number of parts, and drives a moving body linearly, and its drive is precise and quick. The linear motor is widely applied to linear driving devices and positioning devices in all fields such as exposing devices for manufacturing semiconductors, and highly precise machine tools.
In a general liner motor, as shown in FIG. 8, a current is allowed to flow through a coil unit (a moving body in this example) Ci placed between magnet rows Mg opposing to each other (fixed body in this example), and a Lorentz force generated drives the coil unit Ci. The magnet rows Mg are arranged such that the direction of a pair of an N pole and an S pole opposing to each other is altered one by one as shown in FIG. 9. A distance between the closest pairs of N/S poles facing in the same direction is referred as a magnetic pole pitch. A sinusoidal magnetic flux density distribution is generated between the magnet rows Mg where the magnetic pole pitch is one cycle. The magnetic pole pitch after normalization is represented as 2xcfx80.
The individual single coils 2 for constituting the coil unit Ci are in an approximately rectangular ring-like shape (a racetrack shape) as a whole as shown in FIG. 10. Two sides of the four sides of this rectangle opposing to each other in a direction perpendicular to a traveling direction function as a pair of effective conductors 4a and 4b for contributing to generating a thrust force for a moving body in a linear motor. The other two sides opposing to each other form a pair of connecting conductors 6a and 6b for connecting between the effective conductors 4a and 4b, and these parts do not specifically contribute to generating a thrust force for the linear motor.
When a current is allowed to flow through the single coil 2, the directions of the current are opposite to each other between the effective conductors 4a and 4b (indicated as U and U macron). Thus, because the signs of the magnetic fluxes are opposite to each other, when the distance T1 between the effective conductors 4a and 4b is set to a distance corresponding to xcfx80, the thrust force becomes twice as much as that generated on one effective conductor 4a or 4b. 
It is necessary to provide a constant thrust force wherever the single coil 2 may be positioned along the magnet rows Mg for operating the linear motor smoothly. Because the magnetic flux density has the sinusoidal distribution, it is impossible to use one single coil for providing a constant thrust force in whatever way the current may be adjusted. It is necessary to connect the multiple single coils placed with intervals as one pole.
Three phases of (three) single coils 2U, 2V, and 2W are arranged such that their positional phases are displaced by an amount corresponding to (⅔)xcfx80 to one another for using them as one pole in a three-phase excitation motor as shown in FIG. 11. Then, when a current with a phase matching the phases of the magnetic flux densities at the effective conductors 4a and 4b of the individual single coils 2U, 2V, and 2W is allowed to flow therethrough as shown in FIG. 12, a constant thrust force can be obtained even if the positions of the three single coils 2U, 2V, and 2W (a coil unit Ci3 as a whole) move.
On the other hand, two single coils 2A and 2B are displaced by an amount corresponding to xcfx80/2 as a positional phase to form one pole for a two-phase excitation motor as shown in FIG. 13. A distance between the two single coils 2 corresponds to xcfx80, and the single coil itself is identical to that for the three-phase excitation motor. Then, when a current with a phase matching the phases of the magnetic flux densities at the effective conductors 4a and 4b is allowed to flow through the individual single coils 2A and 2B as shown in FIG. 14, a constant thrust force can be obtained even if the positions of the two single coils 2A and 2B (a coil unit Ci2 as a whole) move.
Because three-phase excitation motors can maintain a motor constant (N/W: a thrust force provided with an equivalent current) high, three-phase excitation motors are used more than two-phase excitation motors in general.
However, the two-phase excitation motors can be applied to an area of the applications where the three-phase excitation motors cannot meet a dimensional requirement.
When the three-phase excitation motor or the two-phase excitation motor is structured such that multiple single coils for the individual phases are simply piled up as shown in FIG. 11 or FIG. 13, the distance M3 or M2 between the magnet rows opposing to each other increases, thereby decreasing the magnetic flux density. It is necessary to arrange the effective conductors for the individual phases in a single row, thereby minimizing the distance M2 or M3 between the magnet rows Mg, resulting in constituting an effective linear motor. However, a simple racetrack shape as in FIG. 10 prevents arranging the effective conductors 4a and 4b in a single row because of the existence of the connecting conductors 6a and 6b. There have been different types of proposals for the arrangement while the mutual interference between the connecting conductors 6a and 6b is avoided as much as possible.
Because it is primarily required for the two-phase excitation motors to reduce the size as described before, a method to arrange two single coils 2A and 2B corresponding to the A phase and the B phase separately in the same row while the coils are maintained to have the racetrack shape as shown in FIG. 15 is adopted especially to maintain the distance between the magnet rows as short as possible.
When the two single coils 2A and 2B are separated while their phases in the magnetic flux density are being maintained, they can function as a two-phase excitation motor; A form where single coils are arranged separately is referred as a xe2x80x9cseparate typexe2x80x9d two-phase excitation motor for convenience in the present specification. Though FIG. 15 shows a case where two single coils are separated by (2k+xc2xd)xcfx80(k=1, 2, 3, . . .), the phases of the individual single coils 2A and 2B should be opposed to each other when they are separated by (2kxe2x88x92{fraction (1/2)})xcfx80 as shown in FIG. 16.
FIG. 17 shows an: example of the applications.
A main motor is indicated as a symbol 12 in FIG. 17, and is constituted with a conventional three-phase excitation motor. Because a coil unit 12Ci for the main motor 12 is used with multiple poles in general, a wiring harness 14 for wiring the coil unit 12Ci becomes thick and heavy, and becomes a resistance when the coil unit 12Ci for the main motor 12 travels. Then, a separate type two-phase excitation motor 16 is separately provided such that the motor 16 strides across the main motor 12 to drive the wiring harness 14 in synchronization with the main motor 12 as shown in FIG. 17 (B). Gaps are provided between a case 12a for the main motor 12 and a case 16a for the two-phase excitation motor 16 to prevent a contact between these cases when there is a difference between their travels. Thus, the two-phase excitation motor 16 does not affect the travel of the main motor 12 at all (while the motor 16 moves in synchronization with the motion of the main motor 12). Because the wiring harness 14 is attached to the two cases 16a for the two-phase excitation motor 16, and the wiring harness 14 does not affect the travel of the main motor 12 at all (while the harness 14 moves in synchronous with the motion of the main motor 12).
When a separate type two-phase excitation motor is applied in this way, the separated single coils do not cause any problems, and the separate existence becomes an advantage on the contrary.
Though placing two single coils separately can be used as an application method for the two-phase excitation motors, the predetermined dimensions are specified for the spacing, and the arrangement of them may be very difficult in some cases. Also, a weak thrust force is one of the major disadvantages of the two-phase excitation motors.
The present invention was devised in view of the foregoing, and an object of the present invention is to manufacture a two-phase excitation motor where single coils satisfying a predetermined shape condition are used to form a two-phase excitation motor as xe2x80x9cintegrate typexe2x80x9d, thereby applying it while a magnetic flux density generated by magnet rows is increased as high as possible (in a form for increasing the thrust force).
Another object of the present invention is to provide a two-phase excitation motor which is constituted as a separate type motor using the integrate type coils corresponding to two poles, and can increase a thrust force by an amount corresponding to the increased pole. Still another object of the invention is to provide a two-phase excitation motor which has a shape of a conventional xe2x80x9cseparate typexe2x80x9d two-phase excitation motor, and simultaneously provides a thrust force more than that provided by the conventional separate type two-phase excitation motor.
A two-phase excitation linear motor according to a first aspect of the present invention includes two single coils forming one pole to continuously generate magnetic forces with a predetermined phase interval thereon, the magnetic forces linearly driving a moving body, wherein the two single coils are individually formed as an approximately rectangular ring-like shape where two sides of the rectangle opposing to each other function as a pair of effective conductors for contributing to generating a thrust force for the moving body of the linear motor, and the other two sides opposing to each other function as a pair of connecting conductors for connecting between the effective conductors, parts close to the ends of the effective conductors are bent at an approximately right angle with respect to a coil plane such that the pair of connecting conductors are offset from the coil plane, and extend in parallel with the coil plane where the coil plane is defined as a plane including individual centers of the pair of effective conductors, and the two single coils are integrated into one body such that one of the pair of effective conductors of one single coil is interposed between the pair of effective conductors of the other single coil while the individual single coils are combined such that the offset directions of the connecting conductors of the individual single coils are opposed to each other in a direction perpendicular to a traveling direction. By providing this two-phase excitation linear motor, the above-mentioned problems are solved.
When each of the single coils has a simple racetrack shape, the storage of the individual single coils becomes a problem if the multiple single coils are connected to form a coil unit as described before. Because a two-phase excitation motor has a lower motor constant compared with that of a three-phase excitation motor by nature, and it is senseless to adopt a two-phase excitation motor unless the cost or the size can be reduced, a drive constitution using racetrack-shape single coils as a separate type has been exclusively adopted.
The present invention was intended to devise a shape of a coil to use a two-phase excitation motor not as xe2x80x9cseparate typexe2x80x9d but as xe2x80x9cintegrate typexe2x80x9d as one pole.
The parts close to the ends of the effective conductors are bent at an approximately right angle with respect to the coil plane such that the connecting conductors are offset from (separated in parallel with) the coil plane in the single coil according to the present invention. Then, the two single coils are integrated into one body such that one of the pair of effective conductors of one single coil is interposed between the pair of effective conductors of the other single coil while the individual single coils are combined such that the offset directions of the connecting conductors of the individual single coils are opposed to each other in a direction perpendicular to the traveling direction.
As a result, the individual effective conductors of the two single coils are arranged in a single row, and simultaneously, the length of the offset of the connecting conductors decreases further. Thus, when the single coils are used to form a coil unit, the projected area of the connecting conductors on a transverse section in the traveling direction is decreased further while they are still the integrate type. Also, because the integrate type forms xe2x80x9cone polexe2x80x9d, and a part corresponding to this one pole can form a motor, the size of an entire coil unit can be decreased remarkably.
A second aspect of a two-phase excitation linear motor according to the present invention has a characteristic that the transverse section of the connecting conductors is in an approximately trapezoidal shape including parallel sides approximately perpendicular to the coil plane, and a tilted side opposing to the coil plane and being tilted in a direction opposite to the direction of the offset of the connecting conductors in the extending state. This allows manufacturing a more compact coil unit.
A third aspect of a two-phase excitation linear motor according to the present invention has a characteristic that two or more integrated two-phase (two) single coils are placed in separate positions for multi-polarization.
Though this arrangement embodiment appears similar to that of the separate type two-phase excitation motor, the present invention largely differs from the xe2x80x9cseparate typexe2x80x9d in a point that the individual two coils forms xe2x80x9cone polexe2x80x9d, and the entire device is two-phase multi-polarized, thereby enabling to obtain double thrust force.
A fourth aspect of a two-phase excitation linear motor according to the present invention includes two single coils forming one pole to continuously generate magnetic forces with a predetermined phase interval thereon, said two single coils being placed separately, the magnetic forces linearly driving a moving body. Here, each of the single coils comprises two sub-single coils each formed as an approximately rectangular ring-like shape where two sides of the rectangle opposing to each other function as a pair of effective conductors for contributing to generating a thrust force for the moving body of the linear motor, and the other two sides opposing to each other function as a pair of connecting conductors for connecting between the effective conductors. The two sub-single coils are integrated into one body such that one of the pair of effective conductors of one sub-single coil is interposed between the pair of effective conductors of the other sub-single coil, while the two sub-single coils are connected to each other in series to form one connected-single coil and the two connected-single coils are separately arranged as said single coil for forming one pole.
This arrangement also appears similar to that of the separate type two-phase excitation motor. However, the present invention differs from the conventional xe2x80x9cseparate typexe2x80x9d in a point that the single coil at each location is not a simple racetrack-shape single coil, the single coil (to which any one of the first to third aspects of the invention is applied) is used as a xe2x80x9csub-single coilxe2x80x9d, the single coils are coupled to form a xe2x80x9cconnected-single coilxe2x80x9d, and the two connected-single coils are separately placed to constitute one pole while they serve as the separate type.
Thus, another (connected-) single coil wired in series in the same way is required to form a single pole as a two-phase. excitation motor. Therefore, it also belongs to a category of the xe2x80x9cseparate typexe2x80x9d two-phase excitation motors in terms of the form.
Because two (sub-) single coils are connected in series to form a xe2x80x9cone-phasexe2x80x9d (connected-) single coil in this motor, the number of turns n for each phase is twice as many as that of the single coil according to the conventional, or any one of the first to third aspects of the invention. In general, when the number of turns n increases to obtain a large thrust force, the area of a transverse section of the connecting conductors as well as that of the effective conductors increases, the storage of the single coil becomes degraded, and a dimension in terms of thickness as the single coil increases. Thus, it is unavoidable to increase the distance between the magnet rows accordingly. However, because the individual sub-single coils according to this aspect of the present invention have the number of turns similar to that for the conventional single coil, the dimension in terms of thickness approximately corresponds to that of one sub-single coil, and is not so large. Above all, because it is possible to properly select whether the sub-single coil is used for a single coil or for a connected-single coil, there is an advantage that a simple design change can realize a motor having a different thrust force.